Viral Pathogenesis Flashcards
Common routes of infection and initial sites of replication
- common routes: respiratory, alimentary, or genitourinary tract
- replication: epithelial cells near body surface/barriers
Enterotropic virus definition
replicates in the gut
Neurotropic virus definition
replicates in the nervous system
Factors that determine tropism
- access to desired tissue
- receptors required for virus binding/entry
- expression of host genes required for virus infection and replication
- relative failure of host defenses
Tissue tropism affect on viral development
can drive population variant among or within individuals; particularly in viruses w/highly error-prone replication systems
Transmission and shedding definition
release of infectious particles from an infected host
Site of shedding for local infections
occurs from the site of initial infection
Site of shedding for disseminated/systemic infections
-multiple or distant sites possible
Fomite definition
virus-associated objects
Types of viral transmission
- single susceptible host vs. alternate infection of one host w/another (e.g. insect to human)
- close contact (e.g. enveloped viruses)
- fomites (e.g. hardier, non-enveloped viruses)
- usually horizontal, but may be vertical/germ-line
Immune-mediated pathology associated with viruses
- IMP=viral disease as a result of host immune response to infection
- antibody-mediated (immune complexes)
- cell-mediated (rash, fever, malaise)
- autoimmunity (cross-reactivity)
- immune modulation/suppression
Acute local viral disease: 1. first site of replication 2. viremia 3. secondary replication 4. site of symptoms 5. incubation period 6. duration of immunity 7. Ab responsible for resistance 8. example
- epithelium
- no
- none
- entry epithelium
- 1-3 days
- often short
- secretory IgA
- common cold
Persistent chronic viral infection
- viral infection that continue to produce new virus over long period of time
- result of acute primary infection that is not cleared OR
- virus retains ability to transmit to other organisms or host offspring
Latent chronic viral infection
- substantial periods in which the host produces no detectable virus
- little or no disease in healthy host
- viral genome is silent
- retain the ability to re-initiate transcription and replication to produce new virus
Acute systemic viral disease: 1. first site of replication 2. viremia 3. secondary replication 4. site of symptoms 5. incubation period 6. duration of immunity 7. Ab responsible for resistance 8. example
- epithelium
- yes, primary and secondary
- lymphoid organs, lung, skin
- systemic
- 10-21 days
- usually lifelong
- serum IgG and secretory IgA
- measles
Slow chronic viral infection
- no symptoms on initial infection
- long incubation period
- may or may not induce immune response
- eventual disease followed by progressive deterioration and death
Examples of viral diseases: 1. Acute local 2. Acute systemic 3. Chronic 4. Latent 5. Slow/progressive
- colds, diarrhea 2. smallpox, measles 3. Rubella in neonate 4. VZV in nerves 5. AIDS, canver
General characteristics of chronic viral infection
- ongoing virus infection/replication
- mild or inapparent disease in healthy host
- manifestation of disease often coincides w/immune suppression
Host factors in susceptibility to viral disease
- receptors for virus entry, accessibility and permissivity
- age of host
- genetic background
- immune status
Types of virulence genes (4)
- affect ability of virus to replicate
- modify host defense mechanism
- facilitate virus spread in and among hosts
- directly toxic to host cells
